SOPAC Technical Report 108 September 1990 SWATH-MAPPING TARGET AREAS IN THE EEZS OF TONGA, FIJI, TUVALU, SOLOMON ISLANDS, VANUATU AND PAPUA NEW GUINEA Bernard Pelletier ORSTOM B.P. A5 Noumea Cedex, New Caledonia Prepared for: South Pacific Applied Geoscience Commission (SOPAC) Offshore Programme [3] CONTENTS Page INTRODUCTION .................................................................................................. 5 IDENTIFYING THE AREAS ALREADY MAPPED ........................................ 6 TARGET AREAS IN THE EEZ OF FIJI ................................................................ 6 TARGET AREAS IN THE EEZ OF PAPUA NEW GUINEA ............................ 11 TARGET AREAS IN THE EEZ OF SOLOMON ISLANDS ....................... 13 TARGET AREAS IN THE EEZ OF TONGA ............................................. 17 TARGET AREAS IN THE EEZ OF TUVALU ............................................... 20 TARGET AREAS IN THE EEZ OF VANUATU ............................................... 20 SOME INFORMATION ON NEW SWATH MAPPING SYSTEMS .................... 23 REFERENCES ........................................................................................................ 25 [TR108 - Pelletier] [4] LIST OF FIGURES Figure Page 1 Map showing the navigation of swath mapping surveys in the EEZs of SOPAC countries ............................................. 7 2 EEZ of Fiji showing already mapped area, and proposed areas for future swath map surveys .............................................. 8 3 EEZ of Papua New Guinea showing already mapped areas, and proposed areas for future swath surveys ............................ 12 4 EEZ of Solomon Islands showing the already mapped areas, and the proposed areas for future surveys ........................... 14 5 EEZ of Tonga showing the already mapped areas, and the proposed areas for future surveys ...................................... 18 6 EEZ of Tuvalu showing the already mapped areas, and the proposed areas for future surveys .................................. 21 7 EEZ of Vanuatu showing the already mapped areas, and the proposed areas for future surveys .................................. 22 LIST OF TABLES Table 1 Swath mapping target areas in the EEZs of some SOPAC member countries .............................................................. 26 2 Recommended swath-mapping systems for each selected area ...... 28 [TR108 - Pelletier] [5] INTRODUCTION For the CCOP/SOPAC 17th Session (October 1988) held in Suva, Fiji, Kroenke (1988) prepared a report which emphasised the value of swath-mapping for the identification of potential resources in the Exclusive Economic Zones (EEZs) of SOPAC countries. The report reviewed the main seafloor mapping systems (deep and shallow water, multi-beam echosounders and bathymetric side-scan sonars), indicated the most appropriate system considering the specific objective of the survey, and finally proposed swath-mapping targets in each SOPAC member country. The primary objective of the present report is to identify swath-mapping target areas in the EEZs of some SOPAC member countries in order to plan the second SOPAC swath-mapping cruise for 1990-1991. The first was the GLORIA cruise in August 1989 (Tiffin and others, 1990). This work comes under the SOPAC Offshore Programme and is mainly focused on waters from 500 to 4000-5000m deep. Not all the SOPAC member countries’ waters are reviewed here. This report deals only with the EEZs of Fiji, Papua New Guinea, Solomon Islands, Tonga, Tuvalu and Vanuatu. With the exception of Tuvalu, all of these are countries associated with back-arc basins with resource potential. Back-arc basins are particularly amenable to good results from swath-mapping techniques. Tuvalu, although not part of a volcanic arc, has several large banks in its southern EEZ for which little information exists, and currently has both an active fisheries programme to investigate seamounts, and a boundary delineation programme to determine its legal EEZ. Both these programmes will greatly benefit from swath mapping. The Cook Islands and Kiribati were not included here because although their EEZs are large, they are remote from the island arcs and long costly transits are required to get to these areas. They will be targets for later cruises. Western Samoa and Guam, also not included, have small EEZs. In Guam, the US Geological Survey plans to survey the EEZ with GLORIA, probably in 1992. These latter two countries thus have prospects for good maps already. The target areas proposed in this report have been chosen taking into account the known bathymetry, geological and geophysical data and previous swath mapping surveys and are arranged in alphabetical, not priority, order. The characteristics of each area (location, size, depth, objective and recommended mapping system) are summarised on Figures 2 to 7 and in Tables 1 and 2 (see pages 26 and 28). Only a brief description of each area is given in the text. [TR108 - Pelletier] [6] IDENTIFYING THE AREAS ALREADY MAPPED The first step in identifying future swath mapping target areas is to know the location of areas already mapped. Figure 1 is a compilation of tracklines from various cruises that used swath mapping systems (Seabeam, SeaMARC II and GLORIA) in the EEZs of SOPAC countries. The map has been compiled with the assistance of the Data Management section of the SOPAC Technical Secretariat (Techsec) (Yann Morel and Andre Dauzat). Figure 1 also shows the boundaries of the EEZs of SOPAC countries which can be requested at any scale from SOPAC. The map shows five features: 1. A number of cruises using swath mapping systems have been conducted in the Southwest Pacific since 1984 by Germany (RV Sonne: Seabeam), France (RV Jean Charcot : Seabeam), Japan (RV Kaiyo: Seabeam), Hawaii, USA (RV Moana Wave: SeaMARC II), Scripps, USA (RV Thomas Washington: Seabeam), England (RV Charles Darwin: GLORIA), Australia (HMAS Cook: Seabeam), and SOPAC (HMAS COOK: GLORIA and Seabeam). 2. Most of the areas of full coverage are located in back-arc basins along the active spreading centres or active troughs (Lau Basin, North-Fiji Basin, Vanuatu back-arc Troughs, Woodlark Basin, Manus Basin) although parts of the Tonga and New Hebrides trenches are also covered. Arc areas have received almost no attention. 3. Most of the areas covered are in the EEZs of Tonga, Fiji, Vanuatu and Papua New Guinea. 4. Little swath mapping has been done in the EEZ of Solomon Islands and nothing in the EEZ of Tuvalu. 5. During this compilation, it became apparent that some cruises have not been able to be precisely located due to the lack of good navigational information in SOPAC's database. Consequently, it is recommended that navigation data from the EEZs of SOPAC member countries be sent to Techsec as soon as possible after each cruise. TARGET AREAS IN THE EEZ OF FIJI (Figure 2) The EEZ of Fiji is largely composed of active marginal basins in which active spreading centres, extensional zones and fracture zones exist. Most of the previous swath mapping cruises have [TR108 - Pelletier] [9] been devoted to these active features (Lau Basin, Peggy Ridge, Fiji Fracture Zone and the various tectonic elements of the North Fiji Basin). However, the EEZ of Fiji also comprises the Fiji Platform, the Lau Ridge (a remnant arc), the northern part of the South Fiji Basin (an inactive marginal basin) and, north of the paleo Vitiaz Lineament, a part of the Pacific Plate where seamounts are present. Although large areas have been already mapped by Seabeam, SeaMARC II and GLORIA, numerous future target areas can be identified due to the complexity of the geology of the North Fiji Basin, resulting from the interaction of the Pacific and Indo-Australian plates, and its location between the opposing Tonga and New Hebrides subduction zones. Occurrences of polymetallic massive sulfides associated with the N-S trending spreading ridge have been proved in the central part of the North Fiji basin. Eight areas can be selected in the EEZ of Fiji for future swath mapping surveys. Area FJ 1 Little is known about this area, corresponding to the Koro Sea Basin between Viti Levu and the Lau Group, which is probably quite complex due to the supposed counterclockwise rotation of the Fiji Platform during the opening of the North Fiji Basin. The Hunter Fracture Zone, which may be an old subduction zone and is a sub-active feature, ends in the Koro Sea Basin. The main interest in this area is possibly fishing potential, due to its central position with respect to all the Fijian islands, but this area is given a low priority in comparison with the others. The recommended mapping systems are GLORIA or SeaMARC R. Area FJ 2 This is located just north of the Fiji Platform and is associated with the Fiji Fracture Zone, mapped during the recent SOPAC cruise. An area between the GLORIA tracks and the Vanua Levu Platform, probably part of the Fiji Platform, remains uncharted. This area is interesting for two reasons: fishery potential and completion of the map of the Fiji Fracture Zone. The recommended tools are the SIS 09 or SeaMARC II. Area FJ 3 This is located in the eastern part of the North Fiji Basin along a seismically active tectonic feature composed of ridges and troughs, This feature connects the Fiji Fracture Zone (176'E) and [TR108 - Pelletier] [10] the N-S trending North Fiji Basin spreading centre (21'S) which at this latitude is offset by about 80 km by a fracture zone. Part of this feature, west of Viti Levu, has already been mapped by Seabeam and its